Dual classing, at the moment this is far from needed. There just are not enough classes, but I would still love to see a warrior/mage hybrid or something like that. Of course, that should also mean some disadvantages like not being able to cast spells in heavy armor or something of that effect.

Subclasses, this is something I always like in games. For example say you play a hunter, there could be the option of being a melee focused beast master with an animal companion or a sniper that would make your bow skills insane.